Dynamoelectric machines including metal filled glass cloth slot closure wedges, and methods of making the same

ABSTRACT

A high permeability slot wedge for a dynamoelectric machine with the wedge configured as an elongated bar of uniform cross-sectional configuration formed of a ferromagnetic material having modestly good electrically insulative properties comprising approximately by weight 60% to 80% relatively small ferromagnetic particles such as powdered iron, about 10% reinforcing glass fabric; and 15% to 20% unsaturated thermosetting plastic resin binder such as a polyester resin is disclosed. The ferromagnetic material is homogeneously distributed throughout the thermosetting plastic binder so that the permeability and resistivity of the resulting wedge is substantially uniform throughout.

The present invention relates generally to dynamoelectric machines andmore particularly to such dynamoelectric machines having slot closurewedges and to a method of and apparatus for the manufacture offerromagnetic laminate slot closure wedges

Metal filled composite materials are known and typically employ athermoplastic material such as one of several nylons (polyamide resins).Many types of molded plastic magnets, for example, employ a nylonbinder. Nylons are thermoplastic materials and polymerization iscatalyst initiated. Glass cloth with iron powder imbedded in an epoxybinder (polyether resin) is available commercially from UnitedTechnologies Corporation. Epoxy resins by comparison to thermosetpolyester resins are more expensive and typically slower curing.

The absolute permeability of a material is the ratio of the magneticflux density in a material to the magnetizing force inducing that flux,while the relative permeability of a material is the ratio of theabsolute permeability of such material to that of free space. In eithercase, the permeability of a material is proportional to the ratio of theresulting flux to the magnetomotive force: and the reluctance (magneticresistance) of a material is inversely proportional to its permeability.Air, mylar and most other electrical insulators have relativepermeabilities near unity, and thus are also very poor magneticconductors. There are numerous needs for electrically insulativematerials having a high relative permeability, that is, materials whichare electrical insulators yet good magnetic conductors.

In a dynamoelectric machine having a stator core with inwardly openingconductor slots, the slot opening (i e., air spaces) between adjacentstator teeth is of a relatively high reluctance (low permeability)leading to reduced magnetic flux and a nonuniform magnetic field in theannular gap between the stator and adjacent rotor, the introduction ofundesirable flux harmonics, and sometimes resulting in saturation of thestator tooth tips. It is well known as shown, for example, in U.S. Pat.No. 3,519,862 to provide bore or slot wedges of a low permeabilityinsulating material such as paper or MYLAR to close the slot openingsand insure that the winding segments remain within their individualslots. It is sometimes highly desirable to fill the gap between adjacentstator teeth with a ferromagnetic material, i.e., a material having arelative permeability significantly greater than one.

Electrically insulative ferromagnetic slot wedges have been long known.For Example, in U.S. Pat. No. 1,605,112 high permeability slot closingstrips are formed from ferrous or magnetizable metal woven strands andadditional interwoven strands of insulating material all of which areimbedded in a phenolic condensation product and coated with aninsulating varnish. Only the surface close to the stator bore isprovided with the metal strands in this patented arrangement. U.S. Pat.Nos. 872,824 and 1,684,255 show rolled up iron or steel cloth which isthen formed to a desired shape and permeated with an insulating materialsuch as bakelite. The thus formed bore wedge is insulated from the corestructure by a varnished paper or similar insulator. It is believed thatthe concentration of ferromagnetic material in these patentedarrangements would be less than desired and the relative permeabilitythereof would be correspondingly low. In one currently used technique,electrically insulative ferromagnetic wedges are fabricated from a stackof steel punchings with a polyester resin surface layer molded about thepunchings. These last mentioned ferromagnetic slot or bore wedgesperform their task well, but are relatively expensive to manufacture.Each of these three types of ferromagnetic wedge is heterogeneous in thesense that the resistivity as well as the magnetic permeability is notuniform throughout the wedge, but rather, abruptly changes at themetal-insulator interfaces. Moreover, within the metal portion, theresistivity is relatively low which may give rise to undesirable eddycurrent losses.

It would be highly desirable to obtain the benefits of a ferromagneticslot wedge of a minimum preferred permeability while reducing the costsassociated with such wedges, and to achieve higher concentrations offerromagnetic material in such wedges than attainable by the iron strandor cloth techniques. It would also be highly desirable to retain theadvantages of easy machinability exhibited by thermoplastics such asnylon while achieving the advantages of lower cost, rapid curing time,and inherently higher allowable service temperatures of cross-linkedthermosetting plastics such as those exhibited by many polyester resins.Desirable polyester resins would contain double bonds which would allowcross-linking during polymerization, with such cross-linking giving themgood high temperature properties.

One object of the present invention is to provide an improveddynamoelectric machine slot opening wedge.

Another object of the present invention is the provision of methods andprocesses for fabricating ferromagnetic laminates.

A further object of the present invention is the utilization of thetechnique of the previous object in the manufacture of ferromagneticdynamoelectric machine slot wedges.

A composite slot closing wedge made in accordance with the techniques ofthe present invention exhibits homogeneity with, for example, a relativemagnetic permeability in the range of 3 to 5 throughout. The materialfrom which the slot closing wedges are made displays superior mechanicalproperties such as being easily machined to the desired configurationand finish which properties are very similar to those of TEXTOLITE, awell known phenolic impregnated linen material available from theAssignee herein.

Accordingly, it is a still further object of the present invention toprovide a laminate material having good magnetic characteristics,excellent mechanical properties, ready machinability to close tolerancesand to a smooth surface finish, and high dimensional stability.

Yet a still further object of the present invention is the provision ofa ferromagnetic material having good electrical insulating properties.

Yet another object of the present invention is the utilization of thematerial of either of the previous two objects in the manufacture offerromagnetic dynamoelectric machine slot wedges.

These as well as other objects and advantageous features of the presentinvention will be in part apparent and in part pointed out hereinafter.

In one form of the invention, a dynamoelectric machine has a wounddynamoelectric machine stator core with a generally right circularcylindrical rotor receiving bore and a plurality of slots for receivingportions of electrical coils. There are access openings in the corewhere the slots communicate with the bore for facilitating placement ofelectrical coil portions in the slots. A rotor is journalled forrotation centrally within the bore and the electrical coils, whenenergized, create a magnetic field between the stator and the rotor.Slot closing wedges of uniform cross-sectional configuration along theirrespective lengths are positioned in the core to close the accessopenings subsequent to placement of the coil portions in the slots. Eachof said slot closing wedges is formed from a magnetically conducting,electrically insulating composite material of substantially uniformrelative magnetic permeability throughout the wedge. The slot closingwedges function not only to close the access openings, but also toenhance the uniformity of the magnetic field between the stator and therotor.

In carrying out the present invention in another form thereof, weprovide a method of manufacturing a ferromagnetic motor or generatorstator or rotor slot spanning wedge and a wedge made according to suchmethod. One preferred method includes mixing a powdered ferromagneticmaterial with an uncured unsaturated thermosetting resin to form a pastefollowed by impregnating a carrier fabric, such as glass cloth, with thepaste. Preferably, the impregnated carrier fabric is then compressionmolded to form a preferred shape and the resin is polymerized or cured.In a more preferred form, the ferromagnetic material is powdered ironthat comprises at least 75% by weight of the paste and the thermosettingresin is a polyester resin. Thereafter, the preferred process includesmachining of the formed and polymerized shape and thus transforming theshape into an elongated bar having a generally uniform cross-sectionalconfiguration.

In accordance with a further form of the invention, we provide a wounddynamoelectric machine core having a plurality of slots for receivingportions of electrical coils with access openings in the core forfacilitating placement of electrical coil portions in the slots.Magnetically conducting, electrically insulating composite slot closingwedges function to close the access openings subsequent to placement ofthe coil portions in the slots Each slot closing wedge is ofsubstantially uniform relative magnetic permeability throughout thewedge with that relative magnetic permeability being in the range ofabout 3 to 5. The slot closing wedges are also of substantially uniformelectrical resistivity throughout the wedge with that resistivity beingat least two ohm-centimeters. The wedges may be formed from aferromagnetic material that comprises approximately by weight at least60% ferromagnetic particles having a preselected size range, about 10%reinforcing fabric and at most about 20% resinous binder. Preferably,the material comprises from 60% to 80% ferromagnetic particles and from10% to 20% resinous binder. In one specific preferred form, theferromagnetic particles comprise about 70% of the material.

In accordance with another aspect of the invention, a slot wedge for adynamoelectric machine comprises an elongated bar of uniformcross-sectional configuration and homogeneous composition comprised of aferromagnetic material, such as powdered iron, uniformly distributed ina cross-linked thermosetting plastic binder such as a polyester resin.Preferably, the relative magnetic permeability of the slot wedge iswithin a predetermined range of about 3 to 5 while the resistivity is atleast two ohm-centimeters. The resistivity and relative permeability arerelatively uniform throughout the slot wedge.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a view with parts removed, and parts in section, of a portionof a dynamoelectric machine having no slot wedges;

FIG. 2 is a view similar to FIG. 1 except that the machine includes slotwedges according to the present invention in one form thereof;

FIG. 3 is a somewhat schematic representation of a portion of a processand apparatus useful for fabricating slot closure wedges embodying thepresent invention in one form thereof;

FIG. 3A is an enlarged cross-sectional view of superposed layers ofmaterial at an intermediate stage just prior to entering between thepinch rollers in the process of FIG. 3;

FIG. 4 is a schematic representation of further process steps forfabricating the slot closure wedges of FIG. 2;

FIG. 5 illustrates the configuration of a stator bore wedge of uniformcross-section produced in accordance with the present invention inanother form thereof;

FIG. 6 is a partial perspective view of one of the wedges of FIG. 2;

FIG. 7 is a partial perspective view of part of a motor or generatorembodying the invention in yet another form:

FIG. 8 is a view of an illustrative wedge as in FIG. 6 deployed in astator core of a type for receiving formed coils (coils not shown);

FIG. 9 is an enlarged and exaggerated cross-sectional view of superposedlayers of material after having been subjected to some squeezing betweenthe pinch rollers of FIG. 3;

FIG. 10 is an enlarged and exaggerated cross sectional view ofsuperposed layers of material after having been severed into individualsheets at 105 in the process of FIG. 4;

FIG. 11 is an enlarged and exaggerated cross-sectional view ofsuperposed layers of material subsequent to compression molding in theprocess of FIG. 4; and

FIG. 12 is a magnetization curve for exemplary bore wedge material.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawing.

The exemplifications set out herein illustrate preferred embodiments ofthe invention in specific forms thereof and such exemplifications arenot to be construed as limiting the scope of the disclosure or the scopeof the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1 and 2, end turn portions of the conventional stator windingshave been cut away to better reveal the stator core slot configuration.In FIGS. 1 and 2, the stator cores 10 and 11 are formed from a stack oflaminations or punchings having a plurality of peripherally spacedinwardly opening slots such as 15 and 29 for receiving the coils. Thecoils include illustrative conductor turns as is well known and parts ofwhich are shown as 21, 22, 25, 27 in FIG. 1, and 85, 87 and 89 in FIG.2. The dynamoelectric machines of FIGS. 1 and 2 also include magneticrotors 82 and 13 disposed with the bore of the stator for rotationtherein. A generally uniform annular gap or air space 41 separates thestator cores and the rotors (the relative size of the gap is somewhatexaggerated in FIGS. 1 and 2), and a magnetic field is set up acrossthis gap when the machine is operated.

A comparison of FIGS. 1 and 2 will reveal that, in FIG. 1, conductorssuch as 21 and 27 improperly are located in the radial air gap 41between the rotor 82 and stator 10. It is well known in the art toemploy slot closure wedges to block the openings of the slots andprevent inadvertent movement of coil turns into the air gap as shown inFIG. 1. Such bore wedges are typically are made of polyethyleneterephthalate such as Dupont's MYLAR or similar material and confine thecoils within the slots.

In FIGS. 1 and 2 dotted lines 45 depict the magnetic lines of forcebetween the rotors and stators. It will be noted in FIG. 1 that theselines tend to concentrate near the tip 43 of an illustrative statortooth and to spread therefrom toward the rotor 32. This nonuniformity isdue to the fact that the gaps 17 and 19 between adjacent stator teetheffectively is air or other high reluctance material. Such a nonuniformmagnetic field in the gap 41 may lead to undesired saturation ofportions of the stator, reduce overall efficiency of the machine, andintroduce undesirable harmonics in the air gap flux fluctuations. Theintroduction of slot wedges of conventional plastic type material doesnot improve these magnetic field problems because the slot openingreluctance remains essentially the same as that for air.

In FIG. 2, the lines of force 45 within the gap 41 are generallyuniform. Such uniformity has, in the past, been accomplished, forexample, by providing slot wedges formed of stamped sheet metal andcoated with an insulative material (e.g., by an extrusion process).Wedges 31 and 33 are formed of a metal filled, glass cloth reinforcedlaminate fabricated, for example, by a process to be discussedsubsequently herein.

With reference to FIG. 3, iron powder 47, a polyester resin 49 and achemical thickener 51 (MgO in the specific example to follow) are storedin containers 53, 55 and 57 respectively. These are added in desiredpredetermined percentages to container 59 and thoroughly mixed by mixer61. After mixing, a resulting iron filled polyester paste 68 is conveyedby conduit 65 and applied to glass cloth strips.

One end of a roll supply of woven glass cloth 87 is taped or otherwisefastened to and fed with a one mil (0.001 inch thick) polyethylene filmstrip from film strip roll 69. The polyethylene film acts as a supportor carrier during the process and helps maintain separation betweenlayers of paste impregnated cloth when it is rolled up later in theprocess. The glass cloth strip 3 may be a single layer of fabric ormultiple layers as desired. In a more preferred embodiment, six plies ofBurlington style 3733 30/30 glass fabric are used. The glass fabric andpolyethylene backing merge at the guide roller 77 and continue toward apaste application station. The paste is fed from conduit 65 onto theglass cloth in a controlled manner so that a layer is placed on theglass cloth. The slight buildup of paste at 97 is spread uniformly toabout 0.062 inches in thickness on the glass cloth by a doctor blade 85.Another supply of glass cloth 72 (like cloth 73) is backed with anotherpolyethylene film 101 (like film 99) from roll 71 and, after passingunder the guide or idle roller 79, receives a coating of the paste fromconduit 65 which is also spread to a uniform thickness of about 0.062inches as the superposed strips 75 and 101 pass under doctor blade 67.The paste coated glass fabric and polyethylene film pass around guiderollers 81 and 83 and join with the similarly paste coated glass fabricand polyethylene film from source rolls 87 and 69 (with the paste coatedsurfaces facing one another) and the thus joined layers pass between aseries of pinch rollers at 89 and 90 which squeeze the laminate topromote spreading of the paste and insure that the paste permeates theglass cloth.

FIG. 3A illustrates, in cross-section, an enlarged portion of thesuperposed strips as they enter between the first set of pinch rollers89, 90. Here the facing paste layers have merged into a single layer 95,but extensive movement of the paste into &he glass cloth layers 73 and75 is yet to take place. Additional spreading to insure uniform stripthickness and to squeeze the paste into the cloth interstices occurs asthe strip passes between the successive pairs of pinch rollers.

FIG. 9 depicts in cross-section, an enlarged portion of the superposedstrips after they have passed between the first set of pinch rollers 89,90 and prior to exiting the final set of pinch rollers. In FIGS. 9, 10and 11, the glass cloth layers 73 and 75 have been simplified and shownas single sheets of "windowscreen" woven relatively large fiber strands135, 139, 141, 161 and 163 to better illustrate the migration of thepaste into the glass cloth, while in actual practice, the fibers wouldbe much smaller and more numerous. In FIG. 9, it will be noted that thepaste 95 has moved well into the glass cloth layers, but has not yetpenetrated completely through to the faces of the films 99 and 101 inmost cases. There may remain illustrative voids such as 157 near theouter protective films where, for example, strand 168 which is not inthe plane of the section is still visible behind strand 161, as well asinterior voids or air spaces such as 149. Passage between the remainingpairs of pinch rollers will further distribute the paste fillingadditional ones of the voids such as 157 and reducing the number ofinstances where strands such as 163 are visible, as seen by comparingFIGS. 9 and 10.

The superposed strips 98 exiting the final set of pinch rollers 89, 90are then wound about take-up roller 91 and allowed to thicken. Suchthickening is not the final polymerization, but, rather, is in the formof an increase in the viscosity of the paste from approximately 20,000cps at the time of application to approximately 20×10⁶ before moldingwhich occurs over a period of several days due to the action of thethickener 51. A conventional sheet molding compound machine with itsglass chopping station disabled may be modified and used to implement aportion of the process depicted in FIG. 3.

After adequate thickening or curing, the roll 91 is payed out as shownin FIG. 4 and the two outside layers of polyethylene film 99 and 101 arestripped off. The remaining polyester paste impregnated glass cloth(typically one-quarter inch in thickness or less) is cut into sheets,typically square and measuring twelve inches on a side, by a pair ofcutter blades 103 of for, example, a conventional metal shear, andstacked as at 105 for subsequent processing. Such subsequent processingpreferably is in the form of a compression molding between die pieces107 exerting a force of about 1000 psi. on the composite therebetween toform and finally cure (polymerize) the sheets.

FIGS. 10 and 11 illustrate respectively the comparative cross-sectionsof the 12 by 12 inch sheets prior to and subsequent to the step ofcompression molding. FIGS. 10 and 11 each illustrate two sheets of glasscloth 73 and 75 with paste 95 between the sheets as well as generallypermeating the woven material of the sheets. Each sheet 73 or 75 is, asnoted in the discussion of FIG. 9, illustrated as a "windowscreen" weavewith transverse strands 135 and 161, and longitudinal strands 139 and141, however, in practice several sheets and/or more complex weavingpatterns may be used. Despite passage between the sets of pinch rollers89 and 90, there may, as illustrated in FIG. 10, remain paste-freeregions or voids such as 149 between the glass cloth layers and voidssuch as 151 and 157 where the paste has failed to completely saturatethe glass cloth. Such voids are typically located near the edges of thesheets. Compression molding tends to fill in these few remaining voids.Comparing FIGS. 10 and 11, it will be observed that in FIG. 11, strand163 has become obscured by paste 159 and 165 filling the voids 151 and157. Prior to Compression molding, the sheets in stack 105 are, asillustrated in FIG. 10, about 0.200 inches in thickness while the sheetsin stack 109 subsequent to the compression molding step area, as shownin FIG. 1, about 0.125 inches in thickness. This thickness reduction isaccompanied by a primary lateral flow of the paste to completely fillany voids such as 149 in the region between the glass sheets, along withsome flow to completely permeate the glass cloth eliminating voids suchas 151 and 157, and, perhaps, some overflow or flash at the edges. Suchflash has been found to be small, perhaps one part in eighty, and maysimply be discarded.

The polyester is a thermosetting material and is cured or polymerized byheat and pressure. Curing time is about two minutes at a temperature ofabout 300 degrees Fahrenheit for a pressure of about 1000 psi. At thispoint in the process, a strong magnetic field may be applied to thecomposite if it is desired to create a permanent magnet, however,selection of a more appropriate ferromagnetic material than the ironpowder 47 would be preferable. The cured sheets in stack 109 may besubsequently machined as desired into their final form. Any of thecommonly encountered devices for machining metals may be used to performsimilar machining tasks on the cured sheets.

One preferred final form is the stator slot closure wedge illustrated inFIGS. 5 and 6. The individual sheets in the stack 109 may first besurface machined to smooth the surfaces 113 and 115, and to insure thatthese surfaces are generally parallel. As noted earlier, the compositematerial is easily machined and almost any type of known metal workingdevice may be used in the forming and machining of these sheets. Thesheet is then cut into elongated strips of generally uniformcross-section using a simple metal shear. Typically, the cut stripcross-sectional configuration is rectangular (or trapezoidal if theshear blade introduces a slight taper along the cut edge) with thesmooth opposed flat surfaces forming two opposed elongated surfaces 113and 115 of each strip. The opposed edge convex radii 120 and 121 and theopposed parallel edge surfaces 117 and 119 are then cut into the edgesof the strips by a conventional router. The thus contoured wedge edgesfit snugly between complementarily contoured sides of adjacent statortooth tips as best seen in FIG. 7. The wedge of FIG. 5 is of uniformcross-section and may be about one-tenth inch thick, four-tenths of aninch in width and a length corresponding to the length of the core towhich it is to be applied. The opposed convex surfaces 120 and 121 arepreferably of about three-tenths of an inch in radius.

Wedges as shown in FIGS. 5 and 6 have been inserted between adjacentstator teeth such as 123 and 125 of the stator core 127 of FIG. 7 toprovide greater uniformity of magnetic field in the gap between thestator and rotor as discussed earlier in conjunction with FIG. 2. In thetypical fabrication of stator cores, individual laminations are punchedfrom sheet or strip stock and subsequently stacked one upon another toform a stator core. The die which punches the laminations for statorcore 127 may include arcuate portions for forming the pairs of facingconcavities such as 129 and 131 in adjacent tooth tips for receiving thearcuate portions 120 and 121 of the slot closure wedges. After the sideturn portions of windings such as winding 133 have been positioned intheir respective stator core slots, a slot closure wedge is slid axiallyinto the gap between a pair of adjacent stator teeth to secure the sideturn portion of the winding in place within the slot and tosignificantly reduce the reluctance of the region between those adjacentteeth. The complementarily contoured wedge edges and stator tooth tipsinsure an accurate fixed radial positioning of the wedge in the stator.

FIG. 8 shows a preferred application of the slot closing wedge of FIGS.5 and 6. In motor or generator design where space and particularlystator core slot space is precious, the coils are sometimes formed fromconductors which have a square or rectangular cross-sectionalconfiguration. This shape eliminates the air spaces inherently formedbetween coils of circular cross-sectional configuration and allowspacking of a specified number of turns of specified conductor size intoa smaller slot leaving a maximum amount of iron in the stator. FIG. 8illustrates a parallel sided open slot profile for receiving one or morerectangular conductors. It is known that, in comparison to semi-closedor closed slot profiles, this slot shape facilitates winding placementat the expense of an increase in gap reluctance and high frequencyno-load tooth loss. It has been suggested that these effects may beameliorated by using so-called "semi-magnetic" slot wedges. Theparticular stator 138 shown in FIG. 8 has 72 generally rectangular slotssuch as 140 and 143 equally spaced about an approximately 15 inch bore.One illustrative slot closing wedge 142 is illustrated in positionclosing the slot 143. The coils designed to fill rectangular slots ofthis type are known as "formed coils" and are most commonly encounteredin relatively large integral horsepower dynamoelectric machines.

The following examples illustrate suitable components in percentage byweight which have been employed in accordance with the apparatus andtechnique illustrated in FIGS. 3 and 4 to implement the method andprovide examples of slot closure wedges heretofore described.

EXAMPLE I

    ______________________________________                                        Glass Cloth:                                                                           12.3%   Burlington type 3733 30/30 glass                                              fabric; UM 728 finish; for providing                                          reinforcement.                                               Paste:   68.8%   Hoeganaes 230 Fe powder (atomized)                                    16.7%   MR 14067 isophthalic polyester resin,                                         available from Aristech Resins, Inc.                                  0.4%    Luperox 500R dicumyl peroxide which                                           functions as the initiator or catalyst                                0.3%    USS MgO liquid-dispersed modifier                                             which functions as a thickening agent,                                        available from Aristech Resins, Inc.                                  1.1%    zinc stearate                                                         0.2%    UC A-174 organosilane ester which                                             functions as a coupling agent between the                                     glass and the polyester resin                                         0.2%    UC VR-3, a viscosity reducing agent                          Total:   100.0%                                                               ______________________________________                                    

One foot square sheets about one-eighth inch thick (final machineddimension) manufactured in accordance with this example exhibitedflexural (ASTM D790) and tensile (ASTM d638) strengths of about 27,750and 16,280 psi respectively at room temperature while the correspondingflexural and tensile moduli were 1.5×10⁶ and 1.62×10⁶ psi respectively.These figures drop significantly as temperature is increased, but do notdrop as precipitously as they would if the resin were a thermoplasticmaterial such as a nylon. Again at room temperature, the impact strengthof samples from these same exemplary one foot square sheets measured4.73 foot-pounds per inch by the Izod notch-bar test (ASTM D256).

The percentages in the above Example I were computed based on an assumedpaste loss or flash of about 7.7% due to squeeze-out during thecompression molding step of FIG. 4. Neglecting the glass reinforcement,the above example contains about 78.45% iron powder, 19.05% polyesterresin and 2.5% other components, hence, the ratio of iron to resin isabout 4:1. For preferred results, the paste preferably contains at least75% uniformly distributed powered iron and the final product (includingabout 10% glass fabric) preferably has an iron content, by weight, of60% to 80% with the resin content, by weight, ranging from 15% to 20%.The viscosity of the paste increases as the percentage of ironincreases, however, with the addition of a suitable viscosity-reducingagent such as the above noted Union Carbide VR-3, or with the use of alarger mesh glass fabric ratios greater than 4:1 with correlative higherpermeabilities may be obtained while adequate electrical insulatingproperties are retained with not significant increase in eddy currentlosses. The paste viscosity without viscosity-reducing agents for a 4:1ratio is about 3041 centipoise at the time of initial application to thecloth, and increases to 6480 centipoise for a 4.5:1 ratio and to 13,200centipoise for a ratio of 5:1 at the time of application.

EXAMPLE II

Example II is the same as Example I except that the VR-3 viscosityreducing agent is omitted, the Luperox catalyst is replaced by atertiary-butyl perbenzoate. Sheet size was increased to about two bythree feet and squeeze-out loss dropped to about 1.25%. Tests on slotclosing wedge material made in accordance with this example yielded themagnetization curve of FIG. 12.

From the foregoing, it is now apparent that a novel ferromagneticmaterial as well as a novel stator slot wedge and technique forfabricating such wedges has been disclosed meeting the objects andadvantageous features set out hereinbefore as well as others, and thatnumerous modifications as to the precise shapes, configurations anddetails may be made by those having ordinary skill in the art withoutdeparting form the spirit of the invention or the scope thereof as setout by the claims which follow.

What is claimed is:
 1. A high permeability slot wedge material for useas a slot wedge in a dynamoelectric machine in the form of an elongatedbar of uniform cross-sectional configuration along the length thereof,the material comprising an electrically insulating ferromagneticmaterial comprising approximately by weight: from 60% to 80% relativelysmall ferromagnetic particles; about 10% reinforcing woven fiberglassfabric; and from 10% to 20% cross-linked thermosetting polyester resinbinder uniformly distributed throughout the wedge material.
 2. Theferromagnetic material of claim 1 wherein the small slot wedge particlesare iron and comprise about 70% of the material.
 3. A wounddynamoelectric machine core having a plurality of slots for receivingportions of electrical coils, access openings int he core forfacilitating placement of electrical coil portions in the slots, andmagnetically conducting, electrically insulating composite slot closingwedges for closing the access openings subsequent to placement of thecoil portions in the slots, each of said slot closing wedges being ofsubstantially uniform electrical resistivity throughout the wedge, theelectrical resistivity being at least two ohm-centimeters, and each ofsaid slot closing wedges being of substantially uniform relativemagnetic permeability throughout the wedge, the relative magneticpermeability being in the range of about 3 to
 5. 4. The wounddynamoelectric machine core of claim 3 wherein the core comprises astator having a generally right circular cylindrical rotor receivingbore, the slots communicating with the bore along the access openings,the slot closing wedges functioning not only to close the accessopenings, but also to reduce significantly the reluctance of the corenear the openings.
 5. The wound dynamoelectric machine core of claim 3wherein the slot closing wedges are formed from a ferromagnetic materialcomprising approximately by weight: at least 60% relatively smallferromagnetic particles; about 10% reinforcing woven fiberglass fabric;and at most 20% cross-linked thermosetting polyester resin binderuniformly distributed throughout the wedge.
 6. The wound dynamoelectricmachine core of claim 5 wherein from 60% to 80% of the material is smallferromagnetic particles and from 10% to 20% of the material isthermosetting polyester resin binder.
 7. The wound dynamoelectricmachine core of claim 6 wherein the small ferromagnetic particles areiron and comprise about 70% of the material.
 8. A dynamoelectric machinecomprising:a wound dynamoelectric machine stator core having a generallyright circular cylindrical rotor receiving bore, a plurality of slotsfor receiving portions of electrical coils, and access openings in thecore where the slots communicate with the bore for facilitatingplacement of electrical coil portions in the slots, a dynamoelectricmachine rotor journalled for rotation centrally within the bore, theelectrical coils, when energized, creating a magnetic field between thestator and the rotor, and magnetically conducting, electricallyinsulating composite slot closing wedges each comprising an elongatedbar of uniform cross-sectional configuration along the length thereoffor closing the access openings subsequent to placement of the coilportions in the slots, each of said slot closing wedges being formedfrom an electrically insulative ferromagnetic material including byweight, from 60% to 80% relatively small ferromagnetic particles, about10% reinforcing woven fiberglass fabric, and from 10% to 20%cross-linked thermosetting polyester resin binder, each of said slotclosing wedges being of substantially uniform relative magneticpermeability throughout the wedge, the slot closing wedges functioningto close the access openings and to enhance the uniformity of themagnetic field between the stator and the rotor.
 9. The dynamoelectricmachine of claim 8 wherein the small ferromagnetic particles are ironand comprise about 70% of the wedge-forming material.
 10. Thedynamoelectric machine of claim 9 wherein the relative magneticpermeability of each of said slot closing wedges is in the range ofabout 3 to
 5. 11. The dynamoelectric machine of claim 10 wherein each ofsaid slot closing wedge sis also of substantially uniform electricalresistivity throughout the wedge, the electrical resistivity being atleast two ohm-centimeters.
 12. An insulating slot closing wedge for adynamoelectric machine made according to the method comprising:mixing apowdered ferromagnetic material and an uncured polyester resin to form apaste with the ferromagnetic material forming at least 75% of the pasteby weight: impregnating a carrier fabric with the paste; compressionmolding the impregnated carrier fabric to form a sheet and to polymerizethe resin, the resulting formed and polymerized sheet having a relativepermeability in the range of 3 to 5; and machining the formed andpolymerized sheet to transform the sheet into an elongated bar having agenerally uniform cross-sectional configuration along the lengththereof.
 13. An insulating slot closing wedge for a dynamoelectricmachine as set forth in claim 12 wherein the step of compression moldingincludes the preliminary steps of superposing a protective layer ofinert film on each side of the impregnated carrier fabric and squeezingthe layer protected impregnated carrier fabric to promote spreading ofthe paste throughout the fabric.
 14. An insulating slot closing wedgefor a dynamoelectric machine as set forth in claim 13 wherein the methodincludes the further preliminary step of cutting the layer protectedsqueezed impregnated carrier fabric into individual sheets.
 15. Aninsulating slot closing wedge for a dynamoelectric machine as set forthin claim 14 wherein the step of mixing includes the addition of athickening agent, and further comprising the step of allowing thethickening agent to thicken the paste over a period of time prior to thestep of cutting.
 16. A homogeneous and machinable stator bore wedge madeaccording to the method comprising:mixing a powdered ferromagneticmaterial with an uncured thermosetting plastic resin to form a paste;impregnating a carrier fabric with the paste the impregnated carrierfabric comprising about 10% to 20% thermosetting plastic resin byweight: compression molding the impregnated carrier fabric to form aslab and to polymerize the resin; and machining the formed andpolymerized slab to transform the slab into an elongated bore wedgehaving a generally uniform cross-sectional configuration along thelength thereof.
 17. A stator bore wedge made in accordance with claim16, wherein the step of machining includes forming a pair of relativelysmooth opposed mutually parallel flat surface, cutting the slab intoelongated strips of generally uniform quadrilateral cross-sectionalconfiguration in the direction of elongation and with the smooth opposedflat surfaces forming two opposed elongated parallel surfaces of eachstrip, and contouring the other two opposed flat surfaces to mate withcomplementarily contoured portions of a stator core.
 18. A stator borewedge made in accordance with claim 16, wherein the ferromagneticmaterial comprises at least 75% by weight of the paste and thethermosetting plastic resin is a polyester resin, the method furtherincluding the steps of superposing a protective layer of inert film oneach side of the impregnated carrier fabric, squeezing the layerprotected impregnated carrier fabric to promote spreading of the pastethroughout the fabric, and cutting the layer protected squeezedimpregnated carrier fabric into individual sheets after the second stepand preliminary to the third step.
 19. A stator bore wedge made inaccordance with claim 18 wherein the first step includes the adding of athickening agent, and further comprising the step of allowing thethickening agent to thicken the paste over a period of time prior to thestep of cutting.
 20. A high permeability slot wedge for a dynamoelectricmachine comprising an elongated bar of uniform cross-sectionalconfiguration along the length thereof and formed from an electricallyinsulative ferromagnetic material comprising approximately by weight: atleast 60% relatively small ferromagnetic particles; about 10%reinforcing woven fiberglass fabric; and at most 20% cross-linkedthermosetting polyester resin binder uniformly distributed throughoutthe wedge, said slot wedge being of substantially uniform electricalresistivity throughout the wedge and of substantially uniform relativemagnetic permeability throughout the wedge, the relative magneticpermeability being in the range of about 3 to
 5. 21. A high permeabilityslot wedge material for use as an elongated slot wedge of uniformcross-sectional configuration in a dynamoelectric machine, the materialformed from an electrically insulative ferromagnetic material comprisingapproximately by weight: at least 60% relatively small ferromagneticparticles; about 10% reinforcing woven fiberglass fabric; and at most20% cross-linked thermosetting polyester resin binder uniformlydistributed throughout the material, said material being ofsubstantially uniform electrical resistivity throughout the material andof substantially uniform relative magnetic permeability being in therange of about 3 to 5.